Digital imaging systems, such as those employed for converting still color photographic film (e.g. 35 mm) images into digital format for storage in a digital database and subsequent playback, as by way of a color television monitor, customarily encode the output of an opto-electronic film scanning device to some prescribed resolution and store the encoded image in an associated database as a respective image file. When it is desired to display a particular stored image, the contents of the respective addresses of the database in which the digitized image has been stored are read out and coupled to display driver circuitry for energizing corresponding pixels on the TV monitor. One such system, diagrammatically illustrated in FIG. 1, is described in co-pending patent application Ser. No. 582,305, filed Sep. 14, 1990, by S. Kristy, entitled "Multiresolution Digital Imagery Photofinishing System," assigned to the assignee of the present application and the disclosure of which is incorporated herein. As detailed in that application, photographic images, such as a set of twenty-four or thirty-six 24 mm.times.36 mm image frames of a 35 mm film strip 10, are scanned by a high resolution opto-electronic film scanner 12, such as a commercially available Eikonix Model 1435 scanner. Scanner 12 outputs digitally encoded data (e.g. a 2048.times.3072 pixel matrix) representative of the internal electronic scanning of a high resolution image sensing array onto which a respective photographic image frame of film strip 10 is projected. This digitally encoded data, or `digitized` image, is coupled in the form of an imaging pixel array-representative bit map to an attendant image processing (photofinishing) workstation 14, which contains a frame store and image processing application software through which the digitized image may be processed (e.g. enlarged, rotated, cropped, subjected to scene balance correction, etc.) to achieve a desired image appearance. Once an image file has been prepared, it is stored on a transportable medium, such as a write-once optical compact disc, using an optical compact disc recorder 16, for subsequent playback by a disc player 20, which allows the image to be displayed, for example, on a relatively moderate resolution consumer television set 22 (e.g. having an NTSC display containing and array of 485 lines by 640 pixels per line), or printed as a finished color print, using a high resolution thermal color printer 24.
In the system described in the Kristy application, each high resolution captured image is preferably stored as a respective image data file containing a low, or base, resolution image bit map file and a plurality of higher resolution residual image files associated with respectively increasing degrees of image resolution. By iteratively combining the higher resolution residual image file data with the base resolution bit map image, successively increased resolution images may be recovered from the base resolution image for application to a reproduction device, such as a color monitor (raster type television display) or hard copy printer.
As an example, spatial data values representative of a high resolution 2048.times.3072 (2K.times.3K) image scan of a 24 mm-by-36 mm image frame of a 35 mm film strip 10 may be stored as a respective image data file including a base resolution image bit map file containing data values associated with a spatial image array of 512 rows and 768 columns of pixels and an associated set of residual image files to be stored on the disc. Within the workstation itself, the base resolution image may be further subsampled to derive an even lower resolution sub-array of image values (e.g. on the order of 128.times.192 pixels) for display on a segment of the system operator's workstation for the purpose of identifying image orientation and specifying aspect ratio.
In accordance with an invention described in co-pending patent application Ser. No. 583,265, filed Sep. 14, 1990 by K. Parulski et al, entitled "Mechanism for Controlling Presentation of Displayed Image," assigned to the assignee of the present application and the disclosure of which is incorporated herein, advantage is taken of the information storage capability of an optical compact disc to include on the disc additional presentation control files for each stored image which specifies how the image was captured on film and has been correspondingly digitized and stored on the disc. As a result, when eventually played back, as by way of a high resolution printer or TV display, the image will have an upright orientation and the correct aspect ratio for the display device.
Each image is digitized as though it were horizontally oriented. The digitized image is stored `as is` in the workstation's frame store, and a lower resolution version of the digitized image is displayed on the display monitor of workstation 14, so that the image may be viewed by the operator (photofinisher). As each image is digitized and stored, the system operator, using a workstation input device (e.g. a keyboard or mouse) enters a set of `presentation` control codes that are incorporated within a presentation control file associated with each respective image file, which define how the image was captured on film and has been correspondingly digitized and stored on the disc.
The format of a presentation control file, such as header file 22H associated with image data file 22D, into which normal vertical image frame 22 on film strip 10 has been digitized by scanner 12, is shown in FIG. 2 as comprising an orientation filed 31, an aspect ratio field 33 and a supplemental field 35, in which additional information, such as title, date, etc. may be inserted by the operator in the course of formatting a digitized image for storage on the disc. When the stored image is read from the disc by a playback device, such as an optical compact disc player coupled with a color TV monitor, it reads the presentation control file and causes the played back image to have an upright orientation and the correct aspect ratio for the display device.
Because the video resolution images are decimated versions of high resolution image records from the 35 mm film, the video images can contain more detail than can be displayed using a conventional TV display, reproduction signals for which typically originate with NTSC or PAL format video cameras. Indeed, the 35 mm color film images processed in accordance with the Kristy and Parulski et al systems can be expected to contain a much greater amount of vertical high spatial frequencies than conventional TV images. This additional vertical high spatial frequency content can cause a raster scan display artifact known as "interlace flicker", where the vertical edge details (from sharp horizontal lines, for example) will flicker visibly at a 30 Hz rate on normal interlaced NTSC displays. This interlace flicker occurs because the TV monitor displays every other line of the image during the first 1/60 second field time, and then displays the lines in between during the next 1/60 second field time, as shown in FIG. 3. In regions of an image having significant vertical detail, the lines of the first field will be quite different from the lines of the second field, so these regions of the image will appear to flicker at a 30 Hz rate. The amount of interlace flicker in an image depends on the image content and the way in which the image was photographed.
Interlace flicker can be reduced by lowpass filtering the image in the vertical direction, namely in a direction effectively transverse to the raster scan direction, thus reducing the vertical sharpness of the image. If the image is filtered in this way before it is written to the compact optical disc, the interlace flicker of the TV display can be reduced. Unfortunately, the filter will also reduce the sharpness of color prints made from the digitized images that have been stored on the optical compact disc. Additionally, the quality of the displayed TV images of pictures which were not sharply focused, or those of subjects which do not include significant vertical detail, and therefore will not cause interlace flicker if applied to a TV display, will be reduced without any attendant benefit.